After focusing on an object with the low power objective lens, you are trying to bring it into focus under the 40x objective lens, but the field of view is very dark. Which of the following may remedy this problem?

Choice A rationale: Locates the specimen is incorrect because the fine adjustment knob does not help to find the specimen on the slide, but rather to adjust the focus of the specimen. The fine adjustment knob is a small knob that is located on the side of the microscope, next to the coarse adjustment knob. The fine adjustment knob is used to make small changes in the distance between the objective lens and the specimen, which improves the sharpness of the image.

Choice B rationale: All of the answer choices are correct is incorrect because only one of the answer choices is correct. The fine adjustment knob only fine-tunes the focus of the specimen, not locates the specimen or the focus plane.

Choice C rationale: Locates the focus plane is incorrect because the fine adjustment knob does not help to find the focus plane, but rather to adjust the focus of the specimen. The focus plane is the plane that is perpendicular to the optical axis of the microscope and passes through the focal point of the objective lens. The focus plane is where the specimen is in focus and the image is clear.

Choice D rationale: Fine-tunes the focus is correct because the fine adjustment knob is used to fine-tune the focus of the specimen, which means to make small adjustments in the focus to obtain the best image quality. The fine adjustment knob is used after the coarse adjustment knob, which is used to bring the specimen into approximate focus.

Choice A rationale: Low, high is incorrect because it is the opposite of the direction of simple diffusion. Simple diffusion is the passive movement of molecules along their concentration gradient, which means from high to low concentration.

Choice B rationale: Low, equal is incorrect because it is not the final state of simple diffusion. Simple diffusion will continue until the concentration of molecules is equal on both sides of the membrane.

Choice C rationale: Equal, low is incorrect because it is not possible for simple diffusion. Simple diffusion will stop when the concentration of molecules is equal on both sides of the membrane, and there will be no net movement of molecules.

Choice D rationale: Equal, high is incorrect because it is not possible for simple diffusion. Simple diffusion will stop when the concentration of molecules is equal on both sides of the membrane, and there will be no net movement of molecules.

Choice E rationale: High, low is correct because it is the definition of simple diffusion. Simple diffusion is the passive movement of molecules along their concentration gradient, which means from high to low concentration.